This invention relates to U-tube type heat exchangers, and more particularly, to nuclear steam generators. In U-tube type heat exchangers a first heat exchange fluid is passed into a shell within which a bundle of U-shaped tubes is disposed. Simultaneously a second heat exchange fluid is passed through the tubes. As the first fluid passes over the outer surfaces of the tubes it comes in an indirect heat exchange relation with the second fluid that is passing through the tubes. When the second fluid is at a higher temperature than the first fluid the first fluid is thereby heated, and a portion of the first fluid is converted to vapor. Heated first fluid rises within the heat exchanger, and the vapor is thereafter separated from the liquid phase of the heated first fluid. The liquid phase of the heated first fluid is recirculated within the shell, being returned to the lower portion of the steam generator through a downcomer space defined between the inner wall of the heat exchanger shell and the outer wall of a shroud disposed around the tube bundle. In U-tube type heat exchangers, and especially in nuclear steam generators, the tubes are usually arranged in a closely packed bundle. Due to the close spacing of the tubes, the recirculating first fluid does not always penetrate the tube bundle uniformly. As a result poor thermal hydraulic conditions exist in a region of the tube bundle located just above the tubesheet to which the ends of the U-tubes are attached.
The present invention provides a double plate flow distributor that serves to improve recirculation of the first, or shell side, fluid through the tube bundle and thereby avoids the poor thermal hydraulic conditions associated with U-tube type heat exchangers.